2413 (1 96 1). M. H. Ford-Smith and N. Sutin, J. Am. Chem. Soc., 83, 1830 (1961). N. Sutin and B. M. Gordon, J. Am. Chem. Soc., 83, 70 (1961). J. N. Braddock and T. J. Meyer. J. Am. Chem. SOC., 95, 3158 (1973). J. L. Cramer and T. J. Meyer, Inorg. Chem., 13, 1250 (1974). J. N. Braddock, J. L. Cramer, and T. J. Meyer, J. Am. Chem. Soc.. 97, 1972 (1975). (18) J. C. Solenberger, Ph.D. Thesis, Washington University, St. Louis, Mo., 1969. (19) R. A. Marcus and N. Sutin. Inorg. Chem., 14, 213 (1975). (20) J. Holzwarth and H. Jurgensen, Ber. Bunsenges. Phys. Chem., 78, 526 (1974). (21) I. Ruff and M. Zimonyi, Nectrochim. Acta, 18, 515 (1973). (22) M. Chan and A. C. Wahl, 167th National Meeting of the American Chemical Society, Los Angeles, Calif., April 1974; Inorg. 97. (23) J. N. Braddock. Ph.D. dissertation, University of North Carolina, Chapel Hill, N.C., 1973. (24) S. L. Ross, "Differential Equations", Xerox, Lexington, Mass., 1964, pp 230-233. (25) A. M. Sargeson and D. A. Buckingham, "Chelating Agents and Metal Chelates", F. P. Dwyer and D. P. Mellor, Ed., Academic Press, New York, N.Y., 1964, p 269. (26) A. A. Schilt, "Analytical Applications of 1, 10-Phenanthroline and Related Compounds", Pergamon Press, New York, N.Y., 1969, p 120. (27) R. W. Callahan, F. R. Keene, T. J. Meyer, and D. J. Salmon, J. Am. Chem. SOC.,99, 1064 (1977). (28) R. M. Noyes, Prog. React. Kinet., 1, 129 (1961). (29) R. A. Marcus, J. Phys. Chem., 67,853,2889 (1963);J. Chem. Phys., 43, 679 (1965). (30) H. C. Stynes and J. A. Ibers, Inorg. Chem., IO, 2304 (1971). (31) (a) A. Zalkin, D. H. Templeton, and T. Ueki, Inorg. Chem., 12, 1641 (1973); (b) J. Baker, L. M. Engelhardt, 6 . N. Figgis, and A. H. White, J. Chem. SOC., Dalton Trans., 530 (1975). (32) N. S. Hush, Trans. Faraday Soc., 57, 557 (1961). (33) M. J. Powers, D. J. Salmon, and T. J. Meyer, J. Am. Chem. Soc., 98, 6731 (1976). (34) C. T. Lin and N. Sutin, J. Phys. Chem., 80, 97 (1976). (35) G. S. Laurence and V. Balzani, Inorg. Chem., 13, 2976 (1974)
Nonetheless, the outer-sphere reorganizational barrier should be identical for both reactions (eq 33) as should Z (eq 32). I n the absence of long-range electron transfer in the excited state self-exchange or of significant structural differences either in Ru-N bonds or in the bpy ligands between Ru( b ~ y ) 3 ~and + the excited state, the two self-exchange rates should be identical.
(13) (14) (15) (16) (17)
Acknowledgments. Acknowledgments are made to the National Science Foundation (Grant CHE74- 14405-A02) and to the Materials Research Center of the University of North Carolina under Grant DAHC-04-75-G-0144 with DARPA for support of this research. References and Notes (1) C. R. Bock, T. J. Meyer. and D. G. Whitten. J. Am. Chem. SOC., 96, 4710 (1974). (2) R. C. Young, T. J. Meyer, and D. G. Whitten. J. Am. Chem. Soc., 97,4781 (1975). (3) R. C. Young, C. R. Bock, T. J. Meyer, and D. G. Whitten, J. Am. Chem. Soc., 98, 286 (1976); manuscript in preparation. (4) G. D. Hager and G. A. Crosby, J. Am. Chem. SOC.,97, 7031 (1975). (5) G. D. Hager, R. J. Watts, and G. A. Crosby, J. Am. Chem. SOC.,97, 7037 (1975). (6) K. W. Hipps and G. A. Crosby, J. Am. Chem. SOC.,97, 7042 (1975). (7) R. P. van Duyne and S.F. Fischer. Chem. Phys., 5, 183 (1974). (8) S. Efrima and M. Bison, Chem. Phys Lett., 25, 34 (1974); W. Schmickler, J. Chem. SOC,Faraday Trans., 72, 307 (1976). (9) R. A. Marcus, J. Chem. Phys., 43, 2654 (1965); 52, 2803 (1970). (10) G. Dulz and N. Sutin, Inorg. Chem., 2, 917 (1963). (11) J. D. Miller and R. H.Prince, J. Chem. SOC.A, 1370 (1966). (12) B. M.Gordon, L. L. Williams, and N. Sutin, J. Am. Chem. SOC.,83, 2061
Vibrational Spectra, Resonance Raman Spectra, and Electronic Spectra of the p-Oxo-decachlorodiruthenium( IV) Ion Robin J. H. Clark,* Malcolm L. Franks, and Philip C. Turtle Contribution from the Christopher lngold Laboratories, Uniuersity College, London WCI H OAJ, United Kingdom. Received July 20, I976
Abstract: The infrared and Raman spectra of the complexes K4[Ru2OCllo], Rb4[Ru2OCllo], and Cs4[Ru2OCllo] have been
recorded and the observed bands assigned. The Ru2OCl1o~-ion displays the resonance Raman effect, most spectacularly for the potassium salt, when irradiated with an exciting line whose frequency falls within the contour of the lowest allowed band of the ion at ca. 20 000 cm-I. These spectra are characterized by a large increase in the intensity of the Raman band arising from the ul(Ru-O-Ru), alg. stretching fundamental, together with the appearance of an overtone progression reaching 7ul a t room temperature and 12ul at 100 K for the potassium salt. Six other progressions are also observed in the resonance Raman spectrum of this ion a t room temperature (eight others at 100 K), in each of which it is V I which acts as the progression forming mode. The observation of such progressions has permitted the determination of w ] , X I ] , and several cross terms x l n . The w1 values decrease with increasing size of the cation (decreasing lattice energy), viz. 256.5 (K+), 254.7 (Rb+), and 249.9 (Cs+) cm-l. Excitation profiles for four of the Raman bands have been plotted. That for V I reaches a maximum at ca. 20 000 cm-', from which observation it is concluded that the resonant electronic transition is the axially polarized, electric dipole allowed 'A2, IAI, component of the (e,b)4 (eJ3 (b1,)2 (e,*)' (e,b)4 (eg4) ( b ~ , )(b1J2 ~ transition of the Ru-0-Ru 7-bond system; the observation that the depolarization ratio of V I is =l/3 a t resonance confirms this conclusion. The results suggest the wider use of resonance Raman spectroscopy as a technique for the assignment of electric-dipole-allowed transitions.
-
-
There have been a number of recent reports of the observation of resonance Raman spectra from various inorganic molecules and ions.' Such spectra are characterized, among other things, by a very large enhancement to the intensity of a band arising from a totally symmetric fundamental of the molecule, together with the appearance of high intensity overtone progressions in this same mode. Several metal-metal bonded species which belong, or to a first approximation belong, to the D4h point group, viz. the Mo2Cls4- ion,* the
RezClg2- and Re2Brg2- ions,3 and the carboxylate-bridged species Ru2(02CR)4CI ( R = CH3 or t1-C4Hg),~have been particularly spectacular in this respect; irradiation within the contour of the lowest allowed transition of these formally multiply metal-metal bonded species has led, in each case, to the observation of long progressions in the (axial) metal-metal stretching fundamental, clearly demonstrating that the resonant electronic transition is also axially polarized, and thus of the 6* 6 sort ('Az,, ]AI,).
Clark, Franks, Turtle
-
/
-
Spectra of the p-Oxo-decachlorodiruthenium(IV1 Ion
2474 Form of the PrincipA Co-ordinate
Symmetry
Number
v2
v3
v4
%
'b
v7
08
O=Ru,
Figure 1. The alg and ion.
0.0,
0=0
symmetry coordinates of the Ru20CIi1,"-
The MzOX1o4- ions (X = C1 or Br) represent another class of inorganic species which, where linear, belong to the point group D4h, and which also possess multiple bonds (in this case in the M-0-M part of the ion). The high polarizability of the axial r-bond system should thus render it suitable for Raman and resonance Raman studies. One such species is the Ru2OC11o4- ion, which is known from early x-ray crystallographic work5 to be linear and which has already been the subject of some rather restricted infrared and Raman spectral No attempt has yet been made to assign the visible absorption spectrum of the ion, in which two strong bands (presumably electric dipole allowed) occur a t ca. 20 000 and ca. 23 000 cm-l (the exact frequencies depend slightly on the cation). Overtone progressions have only been observed,] and are only expected to be observed,8 under conditions in which the electronic transition with which the exciting frequency is brought into coincidence is electric dipole allowed. In view of the close relationship between resonance Raman and electronic spectroscopy it seemed possible that if a resonance Raman spectrum could be excited from the Ru20Cllo4- ion, and the progression forming mode identified, the assignment of the absorption bands in the visible region of the spectrum of the ion might be deduced. Accordingly the infrared, Raman, and electronic spectra of the ion have been investigated, as well as the resonance Raman spectra with a variety of exciting lines whose frequencies are in the vicinity of 20 000 cm-I. The ion is, under these conditions, found to display the resonance Raman effect, most spectacularly by the potassium salt; the characteristic feature of the spectra is the observation of (at most) nine progressions, in each of which the ul(Ru-0-Ru) atg fundamental is the progression forming mode. These observations have not only permitted the determination of the various spectroscopic constants UI, X I I , and x l n , but also permitted the resonant electronic transition to be assigned. Journal of the American Chemical Society
Experimental Section Preparation of Samples. The most widely used method for the synthesis of the RuzOC1104- ion is based on that of Woodhead and F l e t ~ h e rwho , ~ employed ruthenium(VII1) oxide as starting material. It is also possible to prepare different salts of the Ru20C1104- ion from the more readily available commercial ruthenium(ll1) chloride. Ruthenium(ll1) chloride (0.5 g) was suspended in concentrated hydrochloric acid (1 2 M). The solution was gently heated for a few minutes and any undissolved solid was filtered off. To the warm solution was added a solution of potassium chloride (0.5 g) in concentrated hydrochloric acid. The resulting solution was allowed to cool, and the red-brown microcrystalline product was separated by suction filtration, washed with absolute ethanol (two 10-cm3 portions), and dried i n vacuo, yield 0.45 g (60%). Anal. Calcd for K ~ [ R u ~ O C I ~ O ] : CI, 48.69. Found: CI, 48.55. The rubidium and cesium salts were prepared similarly using the calculated amount of alkali halide. Anal. Calcd for Rb4[Ru2OCllo]: CI, 37.67. Found: CI, 36.75. Calcd for Cs4[Ru2OCllo]: CI, 32.10. Found: CI, 3 1.6. Instrumental Details. Raman spectra were recorded using a Spex 1401 double spectrometer in conjunction with Coherent Radiation Model C R 12 Ar+ and Model 52 Kr+ ion lasers. The powers of all lines used were in the range 100 mW-2 W. Detection was by means of a cooled RCA C3 I034 phototube (Grade I) with linear response; further details of the system are described elsewhere.2 Spectra were calibrated by reference to the emission lines of neon, which were superimposed directly onto the spectra while they were recorded. Band areas were determined by the trace, cut-and-weigh procedure and then corrected for the spectral response of the instrument. Relative intensities were measured with respect to the 981-cm-' band of potassium sulfate as internal standard. Samples were rotated at ca. 1400 rpm in order to minimize thermal decomposition of the sample at the beam f0cus.l There was no evidence of irradiationproduced decomposition. The frequencies are accurate to 3 ~ 0 . 5cm-' for sharp bands, f 1 cm-l for broader bands, and f 5 cm-' for the broadest bands (given in parentheses). Raman spectra a t liquid nitrogen temperatures were recorded by scanning the laser beam with a rotating glass block across a KCI disk of the compound mounted on a copper finger attached to a Dewar flask. The finger was contained in an evacuated glass envelope. The diffuse reflectance spectra were recorded by use of a Cary 14 spectrometer. Infrared spectra were recorded on a Perkin-Elmer 225 spectrometer down to 200 cm-I and on a FS720 interferometer below 200 cm-'; Nujol mulls were used in each case. The results are accurate to f 2 cm-1.
Results and Discussion Vibrational Analysis. The vibrational representation of the Ru20CI10~-ion, in terms of the D4h point group to which it belongs, is as follows: rvib
= 4alg 4- 2bl,
+ b2g + 4eg + a ] , + 4a2, + bl, + 2b2, + 5e,
Thus the 33 normal modes of vibration of the ion give rise to 1 1 Raman bands (the g modes) and nine infrared bands (the a2, and e, modes). The axial fundamentals of the ion are of particular importance in the subsequent discussion, and accordingly the symmetry coordinates which principally contribute to each normal coordinate of aig and a2, symmetry are sketched in Figure 1. The mode numbering scheme which has been adopted in this paper is also made explicit in Figure 1. The observed infrared and normal (Le., off-resonance, A, = 647.1 nm) Raman bands of the ion, as they occur in the potassium, rubidium, and cesium salts, are given in Table I, together with (as far as is possible) the band assignments. The rule of mutual exclusion is seen to apply, consistent with the centrosymmetric nature of the complex ion. Three of the alg fundamentals have been identified by measurements of the band depolarization ratios (see later). These are ul, u(Ru-0-Ru),,, a t 256.2-249.5 cm-I (the strongest Raman band); u2, u ( R ~ - C I , , ) , ~a~t 293.1-286.4 cm-I; u 3 , ~ ( R U - C I ~a~t 357.2-345.7 ),~~ cm-I.
/ 99:8 / April 13, 1977
2476 Table 11. Wave Numbers and Half Bandwidths of the Members of the c l v l and other Progressions Observed in the Resonance Raman Spectrum of the Complex K4[Ru2OCllo] with 514.5 or 488.0-nm Excitation Max, cm-' RT" LT
Band
258.3 518.7 778.4 I037 1298 1558 1815 2075 2335 2595 2846 (3120) 295.2 553.9 8 14.3 1072 1333 ( 1594)
256.2 5 12.2 768.0 1023 1278 I533 1787
293.1 547.4 801.4 1055
357.2 612.5 867.8 1122 1377
(I
AuIp, cm-' RT" LTh
361.1 623.1 882 I I42 1400 I659 1921 2180 (2441)
R T = room temperature (-295 K).
8 14 22 31 42 55 70
Max, cm-l RT" LT
Band
8
209.8 464.5 719 973 1227
11
14 19 21 27 26 29 30
16 30 40
LTh
8 15 25 36 50
=20? -20? 14 24 28
205.0 467.4 728.2 988 1242 ( 1 500) 1779 2036
312.6 567 927.6 1184 I439 [ 1695)
9 15
10
Auljz, cm-1
RT"
18
12 16
322.1
10 18
935 1194 1453 1712 1977 2227 2483 (2740)
19 25 32 42
10 12 14 18 21 28 28
9 12
10
18 26 37 50
13 16
1865 21 I7 2374 2635 (2896)
15
21 27 26
18
21
152.0 410.0 666
159.0 416.0 672.1
9 II 15
LT = liquid nitrogen temperature (=I00 K).
x5 3v,
2 v l + r / l VI+VP, . . IV
300
400
500
Wavelengthlnm
600
I
700
5
1800
1600
-D
Figure 4. Diffuse reflectance spectra of the complexes K,[RU?OCIIO],
Rb4[Ru2OCI i o ] , and Csd[Ru2OCI I O ] .
I
1400
1
1
loon 800 Wavenumbcr/cm"
1200
1
1
1
1
600
400
200
o
Figure 5. Resonance Raman spectrum of the complex K4[RuzOCIio] obtained with the 5 14.5-nm exciting line of the Ar+ ion laser. Slit widths 100/200/100 fim (spectral slit width 2 cm-I).
+
VI u 9 , which was observed only for the potassium salt; u9 is the 3 12.6-cm-I Raman-active fundamental (belonging to the irreducible representations bl, or e,); (vi) V I U I U I Owhich , reaches a t most C'I = 3,2, and 2 for the K+, Rb+, and Cs+ salts, respectively; the nature of the mode responsible for U I O is not known, but it is unlikely that it arises from an impurity1* in view of the progression with ul and the fact that its excitation profile peaks a t the 20 000-cm-' absorption band; (vii) u l u l u1 1, which reaches a t most V I = 2, 1, and 1 for the K+, Rb+, and Cs+ salts, respectively. The wave numbers and half
+
+
Journal of the American Chemical Society
bandwidths of the members of each progression are given in Table I1 for the potassium salt and Table 111 for the rubidium and cesium salts. The main progression, u 1V I ,and progressions u 1 u1 u2, u I V I u3 and V I U I u4, all involve solely totally symmetric fundamentals, and all seven progressions apparently involve U I as the progression forming mode. This is accordingly the most richly structured resonance Raman spectrum yet observed (Figure 5). The dominance of the a], modes indicates that the
+
/ 99:8 / April 13, 1977
+
+
2417 Table 111. Wave Numbers and Half Bandwidths for the Members of the U I U I and Other Progressions Observed in the Resonance Raman Spectra of Rbd[Ru2OCllo] and C S ~ [ R U ~ O C with I ~ O 514.5-nm ] Excitation
Band
Rb4 [Ru2OCI io1 A u l p , cm-I Max, cm-I RT LT RT LT 254.0 507.0 758.6 101 1 1262
286.4 539.5 349.8 603.6 856.1 1109
2 18.3 471.5
926.6 1180 (1 433)
9 14 22 32 48
254.8 511.3 766.9 1021 1284 1538 1792 2052 292.1 547.8 802.8 1055 356.1 613.4 869 1122 1381 1637 1891
IO 15 9 17 24 36
CS4[RU20C1101 Max, cm-' RT LT
8 13 18 22 28 32 32 35 10 17
249.5 498.6 747.4 996
25 1.O 502.5 753.5 1006 1261 1529 ( 1 798)
10 15 22 36
10 16 24 30 48 58
288.8 537 185
290.8 541.6 793
11 16 22
11 15
9 16 18 25 24
345.7 594.3 842.2
351.0 603.4 854 1106 1357 I611 1854
9 16 22
13 19 25 28 25
19 24 34
18 21 32 33
11
467.1 7 19.8 972 1223 1479 923 1188 1442 1700 1955
466.3 7 12.6 960 1214
16
12 13 20 28 33
18 24 26
924.4 1 172.4 1420
933 1183 1437 1689
652.9 902
642.3 89 1 1140
145.6 403.7
145.6 394.3
enhancement is, in Albrecht's n ~ m e n c l a t u r e , primarily '~ of the A term type, Le., of the type in which the nuclear coordinate dependence of the energy of the resonant electronic state is responsible for the resonance enhancement. A single combination band only of the sort ulvl v g has been observed; the shortness of this progression is undoubtedly because v g is very weak and not totally symmetric; cf. the situation of the AuBr4- ion,I43l5 where short progressions in the alg fundamental have been observed based on one quantum of a nontotally symmetric, but nevertheless Raman-active vibration. (b) Liquid Nitrogen Temperatures. We have also recorded the resonance Raman spectra of the three salts at ~ 1 0 K. 0 The spectra obtained with 514.5 or 488.0 nm exhibited considerably more structure than those recorded a t room temperature. In particular for the K+ salt (Figure 6) nearly all the progressions showed further members; in addition, short progressions were observed based on 2 v 5 and on 2 ~ 1 0in, both of which V I again acts as the progression forming mode. For the Rb+ and Cs+ salts short progressions were also observed of the type U I Y I
+
u2
+ vj.
A Q ~cm-1 , RT LT
+
In general all the bands are narrower a t 100 K than a t room temperature, partly because the contributions of hot bands has been decreased. Most bands occur a t very slightly higher frequencies in the low temperature (KCI disk) spectrum of the complex as compared with the room temperaturr: (pure solid) one. This is a consequence of compressing the solid into a KCI disk and not of the temperature change. Both wave numbers
x5
I
I
,
I 3000
2500
2000
I500
1000
500
UP
I
W
